Hoffman has never really elaborated on why he used a pseudonym for the episode. It’s often speculated by fans that the serious, acclaimed actor was hesitant about being associated with a silly cartoon, but actual commentary from Lisa’s voice actress, Yeardley Smith, implies a different story. Telling her experience of acting alongside Hoffman for the episode, she said: 

“I think people sometimes think of voice-over as being a lesser form of acting because nobody sees your face, but I’ve never felt that way. I would say certainly on that day with Dustin Hoffman, it didn’t seem like he felt that way either.”

Hoffman wasn’t the only celebrity to avoid being credited. In season 3, Michael Jackson voiced a character who was pretending to be Michael Jackson, but when that character started singing, Jackson had another soundalike actor sing on his behalf. It was an absurdly weird and complicated guest star situation, although one that fits on a meta level; just as there’s a lot of confusion among the Simpson family about who this character really is, there was also plenty of confusion from the audience over whether they were actually hearing Michael Jackson.